In on-line services or communities, it is common to offer some kind of rating system. For example, an on-line marketplace can allow its participants to rate buyers or sellers (e.g., “rate your experience with this seller on a scale of one to ten”), or to rate specific items, services, businesses, etc. Question-and-answer services may allow participants to rate each other based on how well they answer questions. A user of such a service, or a participant in the community, normally has the opportunity to view the ratings. Thus, a buyer in an on-line marketplace who is contemplating entering into a transaction with a particular seller can obtain a report on other people's experience with the seller, such as “previous buyers have given this seller an average rating of 8.7 on a scale of one to ten.”
In a community that is not on-line, people have traditionally sought information about services, merchants, items, etc., through recommendations of friends or acquaintances. Due to the trust that may be established through a pre-existing personal relationship, a person may place more weight on opinions offered by friends and acquaintances than he or she would place on the opinions of strangers. Thus, if a person is seeking opinions on a car dealer, a building contractor, a restaurant, etc., he or she may be more likely to put trust in the opinions of his or her friends or acquaintances than in the public at large. On-line rating systems typically provide ratings that are partly or wholly based on the opinions of people who are unknown to the person who is using the rating.
Moreover, ratings in on-line rating systems are often subject to certain systemic biases. For example, in an on-line marketplace, a buyer may be given the chance to rate a seller once per transaction, so the aggregate rating of the seller may be skewed toward the opinions of buyers who buy frequently from that seller. Additionally, cliques of participants in the marketplace (or in any other community in which ratings are offered) can agree to rate each other highly, thereby artificially inflating each other's overall ratings. Regardless of the circumstances under which a rating is generated, on-line rating system generally encourage those seeking information to rely on the opinions of strangers, which is not in line with the traditional practice of seeking word-of-mouth advice from those whom one knows.